US President Donald Trump announced on Twitter on Tuesday he had fired his National Security Adviser John Bolton, a key figure on issues involving Australia, including the US-led maritime security mission in the Strait of Hormuz and concerns about Chinese technology company Huawei.

Mr Trump and Mr Bolton traded Twitter messages on Tuesday offering different versions of the exit.

"I informed John Bolton last night that his services are no longer needed at the White House," Mr Trump wrote in his tweet.

"I disagreed strongly with many of his suggestions, as did others in the Administration."

Mr Bolton responded with a tweet: "I offered to resign last night and President Trump said, 'Let's talk about it tomorrow'."

White House Spokesman Hogan Gidley declined to explain the different versions of the firing.

Mr Gidley did say Charlie Kupperman would be the new acting national security adviser.

Adding to the confusion, the White House released an updated schedule of events on Tuesday morning and it included Mr Bolton joining Secretary of State Mike Pompeo and Treasury Secretary Steve Mnuchin for an afternoon press briefing.

Mr Bolton only took up the role in April last year.

He was the president's third national security adviser in less than three years, with former lieutenant general Michael Flynn lasting just 24 days before resigning over his communications with Russia, and retired lieutenant general HR McMaster's term ending after just over a year.

The drama comes ahead of Mr Morrison's much-anticipated visit to Washington DC, which includes Mr Trump hosting the prime minister with a state dinner on September 20.

Mr Bolton, a renowned hawk on Iran, China and North Korea, has been a highly visible figure in US-Australian relations.

When Mr Morrison and Mr Trump dined at the G20 in Osaka in June, Mr Bolton was at the table.

Analysis by the Brookings Institution points to 77 per cent turnover in Mr Trump's senior advisers.

"I'm legitimately shaken by the grave instability of American foreign policy today," Democrat Senator Chris Murphy, a member of the Foreign Relations Committee, wrote on Twitter.

"I'm no Bolton fan, but the world is coming apart, and the revolving door of US leadership is disappearing America from the world just at the moment where a stable American hand is most needed."

In recent months, tensions have risen between Bolton and US Secretary of State Mike Pompeo over influence in the president's orbit and how to manage the president's desire to negotiate with some of the world's most unsavoury actors.

Since joining the administration in the spring of last year, Bolton has espoused scepticism about the president's whirlwind rapprochement with North Korea, and has advocated against Trump's decision last year to pull US troops out of Syria.

He masterminded a quiet campaign inside the administration and with allies abroad to persuade Trump to keep US forces in Syria to counter the remnants of the Islamic State and Iranian influence in the region.

Mr Bolton was also opposed to Trump's now-scrapped notion to bring Taliban negotiators to Camp David last weekend to try to finalise a peace deal in Afghanistan.

South Carolina Senator Lindsey Graham, who was travelling with Trump Monday, said reports of Mr Bolton's dissent on the Taliban meeting were a "bridge too far" for Trump.

One Republican familiar with the disagreements between Mr Trump and Mr Bolton said the adviser's opposition to a possible meeting between Trump and Iranian President Hassan Rouhani was a precipitating factor in the dismissal.

Mr Bolton was a chief architect of Mr Trump's tough stance on Iran and he called for hardline approaches against North Korea, Russia and Afghanistan.

Mr Bolton's departure followed his reported opposition to Mr Trump's controversial plan to bring Taliban negotiators to Camp David last weekend to try to finalise a peace deal in Afghanistan.

Australian Associated Press